AUTHOR=Li Hong , Zhou Bin , Liao Ping , Liao Daqing , Yang Linghui , Wang Jing , Liu Jin , Jiang Ruotian , Chen Lingmin 

TITLE=Prolonged exposure of neonatal mice to sevoflurane leads to hyper-ramification in microglia, reduced contacts between microglia and synapses, and defects in adult behavior

JOURNAL=Frontiers in Neurology

VOLUME=Volume 14 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/neurology/articles/10.3389/fneur.2023.1142739

DOI=10.3389/fneur.2023.1142739

ISSN=1664-2295

ABSTRACT=Background: Prolonged exposure to general anesthetics during development is known to cause neurobehavioral abnormalities, but the cellular and molecular mechanisms involved are unclear. Microglia are the resident immune cells in the central nervous system and play essential roles in normal brain development. 
Materials and Methods: Seven-day-old C57BL/6 mice were randomly assigned to 2 groups. In the SEVO group, mice were exposed to 2.5% sevoflurane for 4 hours. In the Control group, mice were exposed to carrier gas (30% O2/70% N2) for 4 hours. Fixed brain slices from P14 and P21 mice were immunolabeled for ionized calcium-binding adapter molecule 1 (IBA-1) to visualize microglia. Morphological analysis of microglia in the somatosensory cortex was performed using ImageJ and Imaris software. Serial block face scanning electron microscopy was performed to assess the ultrastructure of the microglia and the contacts between microglia and synapse in P14 and P21 mice. Confocal imaging of brain slices was used to assess microglia surveillance in resting and activated states in P14 and P21 mice. Behavioral tests were used to assess the effect of microglia depletion and repopulation on neurobehavioral abnormalities caused by sevoflurane exposure.
Results: Prolonged exposure of neonatal mice to sevoflurane induced microglia hyper-ramification with an increase in total branches length, arborization area and branch complexity 14 days after exposure. Prolonged neonatal sevoflurane exposure reduced contacts between microglia and synapses, without affecting the surveillance of microglia in resting state or respond to laser-induced focal brain injury. These neonatal changes in microglia were associated with anxiety-like behaviors in adult mice. Besides, microglial depletion before sevoflurane exposure and subsequent repopulation in the neonatal brain mitigated anxiety-like behaviors caused by sevoflurane exposure.
Conclusions: Our experiments indicate that general anesthetics may harm the developing brain, and microglia may be an essential target of general anesthetic developmental neurotoxicity.